The properties required for a copper alloy material to be used for the uses in electrical or electronic equipments include, for example, electrical conductivity, proof stress (yield stress), tensile strength, bending property, and stress relaxation resistance. In recent years, the demanded level for those properties becomes higher, concomitantly with the size reduction, weight reduction, enhancement of the performance, high density packaging, or the temperature rise in the use environment, of electrical or electronic equipments.
Conventionally, in addition to iron-based materials, copper-based materials, such as phosphor bronze, red brass, and brass, have also been widely used in general as the materials for electrical or electronic equipments. These copper alloys acquire enhanced strength through a combination of solid solution strengthening of tin (Sn) or zinc (Zn) and work hardening based on cold working such as rolling or drawing. In this method, since the electrical conductivity is insufficient, and high mechanical strength is obtained by making a cold working ratio high, the bending property or stress relaxation resistance is lowered.
As a strength-enhancing method for replacing this, in addition to the combination of solid solution strengthening and work hardening, precipitation strengthening is available by which a fine second phase is precipitated in the material. This strengthening method has advantages of enhancing the strength as well as simultaneously enhancing the electrical conductivity, and accordingly, this strengthening method has been implemented with many alloy systems.
Among them, a Cu—Ni—Si-based alloy which is strengthened by finely precipitating compounds of nickel (Ni) and silicon (Si) in copper (Cu) (for example, C70250 as a CDA [Copper Development Association]-registered alloy) is high in strength, and is widely used. Furthermore, a Cu—Ni—Co—Si-based alloy or a Cu—Co—Si-based alloy, in which a part or the entirety of Ni is substituted with cobalt (Co), has an advantage of having higher electrical conductivity than the Cu—Ni—Si system, and these alloys are being used in some applications.
However, along with the recent downsizing of the parts to be used in electronic equipments or automobiles, the electric/electronic parts to be used are subjected to bending at a smaller radius, and thus there is a strong demand for a copper alloy material high in mechanical strength and excellent in bending property. In order to obtain high strength in the conventional Cu—Ni—Co—Si system or Cu—Ni—Si system, potent work hardening may be utilized to enhance the strength by increasing the working ratio in rolling, but this method deteriorates bending property as described above, and thus a good balance between high strength and satisfactory bending property cannot be achieved.
In regard to this demand for enhancement of bending property, some proposals are already made to solve the problem by controlling crystal orientation. It has been found in Patent Literature 1 that in regard to a Cu—Ni—Si-based copper alloy, bending property is excellent when the copper alloy has a crystal orientation such as that the grain size and the X-ray diffraction intensities obtained from {3 1 1}, {2 2 0} and {2 0 0} planes satisfy certain conditions. Further, it has been found in Patent Literature 2 that in regard to a Cu—Ni—Si-based copper alloy, bending property is excellent when the copper alloy has a crystal orientation in which the X-ray diffraction intensities obtained from {2 0 0} plane and {2 2 0} plane satisfy certain conditions. It has also been found in Patent Literature 3 that in regard to a Cu—Ni—Si-based copper alloy, excellent bending property is obtained by controlling the ratio of the cube orientation {1 0 0} <0 0 1>.